1. Field of the Invention
The invention relates generally to lensed fluorescent troffer lighting fixtures and particularly to a combination door frame and light trap which mounts the lens cover to the fixture, the door frame being readily opened to gain access into the interior of the fixture.
2. Description of the Prior Art
Fluorescent lighting has long been commonly employed in commercial, institution and industrial applications due primarily to energy efficiencies inherent in the operation of fluorescent fixtures and the relatively low fixture cost associated with the need for large numbers of such fixtures in such applications. Fluorescent lighting fixtures suitable for such applications must also be of pleasing appearance and must provide a desired quality of light including adequate light for task lighting applications inter alia. Fluorescent lighting in the form of lensed fluorescent troffer lighting fixtures have long provided acceptable lighting solutions in office environments and the like, such applications requiring literally thousands of such lighting fixtures mounted by suspended ceiling grid arrangements and the like to provide desirable lighting performance and desirable aesthetics. Lensed fluorescent troffer lighting fixtures can also be surface mounted in those applications requiring such mounting and can provide excellent performance in such applications. In recessed applications, however, the space within which lighting fixtures are to be mounted has become increasingly smaller, these applications typically being referred to as reduced plenum installations, it being necessary to provide a fluorescent troffer lighting fixture of reduced volume and particularly of reduced depth to allow ready mounting within reduced plenums while retaining desirable performance characteristics such as minimal lamp image with desirable light outputs. Within this context, the need to provide fixtures which can be manufactured at minimum cost and high performance has increased. Such fixtures must be capable of manufacture with low material costs, low labor costs and must be capable of shipment to a job site with cost efficiencies. Once at a job site, such low-cost, high performance fixtures must be capable of rapid installation while continuing to provide ever-increasing energy efficiencies. Lensed fluorescent troffer lighting fixtures must therefore provide a marriage of aesthetic and performance considerations at minimum manufacturing and shipping costs. When in use, both grid-type and specification premium lensed fluorescent troffer lighting fixtures are seen by occupants of a space being illuminated primarily as prismatic lens covers surrounded by a reveal which in essence comprises portions of a door frame which mounts the lens cover in a desired relationship to lamping contained within the fixtures. As is commonly practiced in the industry, the door frame is structured to provide a minimum reveal consistent with appropriate mounting of the door frame to remaining portions of a fixture. Due to aesthetic considerations, latching structure which allows the door frame to be opened and thus to gain access into the interior of the fixture must be unobtrusive and preferably be of a low profile which is not perceived by an occupant of the space being illuminated. Lensed fluorescent troffer lighting fixtures also must be designed to obscure lamp images, such obscuration being a function not only of a prismatic lens cover but also of the fixture itself. Use of T8 lamping and relatively low profile electronic ballasts facilitate the design of lensed troffers of lesser height dimensions and which are capable of mounting within reduced plenum situations. Fixtures of this type must be provided with door frames of relatively low profile and which are configured to avoid the use of separate fastening elements in the manufacture of the door frame. Further, light leaks about interfaces between the housings of lensed troffer fixtures and door frames must be prevented in order to provide a desirable appearance. A door frame for a lensed troffer fixture must also be readily openable by manipulation of latches which are available for manual manipulation from beneath the fixture while being visually unobtrusive. On opening of a door frame for a lensed troffer fixture, it is further desirable for the door frame carrying the lens cover to remain in place and attached to remaining portions of the fixture during the time when access to the interior of the fixture is necessary such as for relamping or other maintenance.
An example of a lensed fluorescent troffer lighting fixture is seen in U.S. Pat. No. 3,045,577 to Lazerson. Lazerson describes a door frame which carries a lens cover. Lazerson does not provide structural components comprising a door frame which can be assembled together by means of fastening elements integrally formed with the structural components. In U.S. Pat. No. 3,988,609, Lewin describes lensed troffer lighting fixture including a lighting panel or prismatic lens cover described as exhibiting substantial efficiencies, the fixture itself apart from the lens cover not being improved relative to the prior art.
In U.S. Pat. No. 5,823,663, Bell et al describe a fluorescent troffer lighting fixture and particularly a parabolic troffer formed of a housing assembly comprising structural components capable of snap-fit assembly. Kaiser et al, in U.S. Pat. No. 5,806,972, describe a light trap and louver mounting arrangement useful with the housing assembly disclosed in the Bell et al patent. The parabolic troffers disclosed by Bell et al and Kaiser et al relate to the present lensed fluorescent troffers only in the similar concept of providing structure capable of snap-fit assembly without the need for separate fasteners, the particular structures of the present lensed troffers including the present door frame and light trap combination differing from corresponding structures as disclosed in the Kaiser et al and Bell et al patents.
The invention thus provides a door frame for a lensed fluorescent troffer lighting fixture wherein the door frame is capable of snap-fit assembly of structural body elements without the need for separate fasteners. The structural body elements of the invention which form the present door frame and light trap combination are provided with fastening elements which are integral with the body elements, thereby yielding savings in material costs as well as in assembly costs while providing a door frame and light trap combination having excellent mechanical performance as well as being aesthetically pleasing and which can be mounted to fixture housing assemblies of varying description including housing assemblies of lensed troffer lighting fixtures formed with a minimum depth to allow installation in reduced plenum environments while retaining desirable performance characteristics including reduction of lamp image and production of desired illumination levels. The door frame of the invention provides necessary functions such as the mounting of a prismatic lens cover to a housing assembly of a lensed troffer fixture while also providing a light trap function, the present door frame being readily manufactured at low cost while being capable of pleasing appearance when in use.